Add PRD to steel thread skill

[TRahulSam1997]

Why

Product PRDs describe what to build, but technical planning benefits from first identifying the thinnest end-to-end steel thread and then sequencing the remaining scope as demo-ready vertical slices. This skill creates that bridge without embedding organization-specific domain knowledge.

Parallelism must be considered while slices are formed, not added after technical tasks are generated. Capturing Dev+agent pair capacity, dependencies, safe parallel groups, and synchronization points in steel-thread.md gives Spec Kit /speckit.plan or an equivalent SDD planning step the delivery constraints needed to produce an executable design without forcing unsafe concurrency.

What changed

• adds the host-agnostic prd-to-steel-thread skill
• produces steel-thread.md with a solo steel thread, demo-ready slices, JIT infrastructure, and capacity-aware parallelism
• includes generic PRD and steel-thread templates
• adds an SDD planning/design hand-off that supports Spec Kit and other workflows
• documents the skill in the toolkit catalogue

[TRahulSam1997]

Engagement example of skill being used on a real feature that was shipped.

Running agent with skill

Running.agent.with.skill.mov

Internal agent asking human questions (guided by skill)

Ravi.asking.human.questions.guided.by.skill.mov

Internal agent asking human questions for further clarification after creating steel thread doc

Ravi.asking.human.questions.for.further.clarification.after.creating.steel.thread.doc.mov

Steel thread ready!

The next step is to run /speckit.plan on a fresh agent and feed this steel thread MD file along with the PRD to begin the build process 🔨

Usually the PRD itself is fed into /speckit.specify as that's product oriented whereas /speckit.plan is the technical implementations steps.

[bsigney]

Really like this. What makes it work for me: steel thread as Slice 0 and solo before anything fans
out, infrastructure only in the slice that exercises it, and "capacity is a ceiling, not a target" —
that last one is the opposite of how most plans get written. Flat Slice 0..N instead of lanes and
1a/1b keeps it readable too. Repo side's clean: validate passes, links stay inside the skill,
README row's there.

Just a few inconsistencies to sort out — mostly the same rules written in several places, and a
couple have already drifted apart from each other. Comments inline.